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Planck: Dust Emission in Galactic Environments

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Planck: Dust Emission in Galactic Environments Planck’s impact on interstellar medium science new insights and new directions Peter Martin CITA, University of Toronto On behalf of the Planck collaboration Perspective Wasted opportunity Fractionally, there are not many baryons, and even though Planck has given us a bit more, still most of these baryons are not in galaxies. Extragalactic context: Ellipticals Elliptical galaxies: red and dead. Very little ISM: gas and dust used up and/or expelled. NGC 4660 in the Virgo Cluster Hubble Space Telescope Elliptical envy With no ISM – no Galactic foregrounds – imagine the clear view of the CMB from inside such a galaxy! Galactic centre microwave haze Planck intermediate results. IX. Detection of the Galactic haze with Planck Here be monsters Non-thermal emission. Relativistic particles. Extragalactic context: Spirals Spiral galaxies: gas and dust available in an ISM for ongoing star formation NGC 3982 HST Dusty disk – like we live in Spiral galaxy: edge on, dust lane In our Galaxy, a foreground to the CMB. NGC 4565 CFHT An overarching question in interstellar medium (ISM) science Why is there still an ISM in the Milky Way in which stars are continually forming? How does the Milky Way tick? Curious Expeditions: Augustinian friar’s astrological clock. Spirals: gratitude Would we be able to figure out, ab initio and theoretically, how stars form, if we did not have an ISM “up close” in the Galaxy and so the empirical evidence and constraints? Or more to the point, could we answer why star formation is so disruptive of the ISM and so inefficient? Or would we have any fun at all? An ISM research program Galactic ecology: the cycling of the ISM from the diffuse atomic phase to dense molecular clouds, the sites of star formation/evolution, and back. Because of feedback, recycling, and infall, current star formation is not all-consuming, and there still is an ISM. Comprehending complexity in the Galactic ISM, from ethereal wisps to dense structures at the onset of star formation. Details are intriguing too Planck provides full sky coverage, for global analysis. But Planck also enables regional analyses, to find evidence for astrophysically important processes. Why Planck will impact ISM science Planck Legacy Archive Separated components – XII PCCS – XXVIII PSZ – XXIX CO -- XXIII Dust tau and T – Explanatory Supplement The reservoir for star formation Planck measures the reservoir Previous talk by Miville-Deschênes W3: a star-forming Giant Molecular Cloud W5 W4 W3 from Canadian Galactic Plane Survey: H I channels and radio continuum (J. English) W3 GMC Planck dust optical depth at 5’ resolution ~ 2 degree field Miville-Deschênes earlier talk W3 GMC Herschel: Blue 70 μm Green 160 μm Red 250 μm ESA enhanced rendition: see Herschel latest news Rivera-Ingraham et al. 2013, HOBYS Herschel KPs: surveys of known star-forming molecular clouds and the Galactic plane Herschel studies at higher resolution in targeted molecular clouds: Gould Belt GBS: Andre et al. 2010 High-mass stars HOBYS: Motte et al. 2010 Also a Galactic plane survey, full 360 degrees in longitude, but |b| < 1 degree. Hi-GAL: Molinari et al. 2010 Herschel image offsets To measure total dust intensity (and ultimately study τν and β) all Herschel images need a zero- point offset, as can be provided by a combination of Planck in the submillimetre and IRAS in the far infrared. Bernard, Paradis, et al. 2010 P63: Schulz (implementation in SPIRE pipeline in HIPE 10) Planck cold clumps blind survey Blind all-sky survey (C3PO). Compact regions colder than their surroundings; possible early stages leading to star formation. Planck early results. XXIII. The first all-sky survey of Galactic cold clumps Follow-up with Herschel: Planck early results. XXII. The submillimetre properties of a sample of Galactic cold clumps Juvela, Ristorcelli, et al. 2012 Session 12 talk by Montier Origin of this high density structure Review: Hennebelle and Falgarone 2012 “Turbulent” structure “Column density” maps reveal complex structure. The 1-D power spectrum of the image is a power law, decreasing to high spatial frequency (small scales). Broadly suggestive of a turbulent influence (with magnetic fields). Numerical simulations needed to follow the physics and chemistry. Characterizing structure – dust Mask power spectrum difference from dust emission. corresponds Planck 2013 results XV: to PS index CMB power spectra and likelihood –2.6 Check against power spectrum of gas Single frame from an H I spectral data cube (NEP) Lots of structure, changing with velocity 12 degrees Rendered H I cube to show different LSR velocity ranges Dust is well correlated with the LVC and IVC gas: Planck early results. XXIV. Dust in the diffuse interstellar medium and the Galactic halo CMB High HVC, no dust Intermediate You IVC Low G86 field LVC 5 x 5 degrees Characterizing structure – H I Power spectrum of H I column IVC index -2.7 density, LVC and IVC. Effect North LVC index -2.8 of beam Ecliptic Pole, 12 x 12 deg. Noise Analysis of GBT data: Stefan, Martin, et al. 2013 k = 0.001 k = 0.1 arcmin–1 Index for different parcels of gas, many different linear scales LVC black IVC red HVC cyan LVC+IVC (~ expectation for Planck dust ) – 2 – 3 NEP Various fields From a diffuse medium to condensed structures Two major transitions: 1) From warm neutral gas (WNM) to cold H I (CNM), via thermal instability. Study numerically to see what fraction is in each form and what conditions would give rise to the observed power spectrum index ~ – 2.6. Saury, Miville-Deschênes, et al. 2013. 2) Atomic to molecular gas, with CO cooling to even lower temperatures. Planck CO. What is the role of the magnetic field in determining the structure? Planck all-sky CO product CO emission integrated over velocity: W(CO). Out of the Galactic plane, CO emission extends well beyond the known boundaries of molecular clouds, providing an opportunity to study the transition region where gas is becoming molecular. And the nature of the “dark gas.” Planck 2013 results. XIII. Galactic CO emission Session 7 talk by Combet (including PIP #58) “Dark gas” phenomenon “Excess” dust emission, dust optical depth not correlated with detectable gas tracers, H I or CO. Planck early results. XIX. All-sky temperature and dust optical depth from Planck and IRAS – constraints on the “dark gas” in our Galaxy. Also Session 12 Grenier. Possible reasons for “excess:” transition phase where H2 (invisible) survives photodissociation but CO does not. X(CO) is higher than assumed: CO-dim gas; more gas (dust) than traced. atomic gas underestimated due to self-absorption of H I line in relatively cold gas; more dust than traced. dust with higher opacity/H than standard assumed; no extra “dark” gas or dust. Opacity: ability of a parcel of ISM material to emit Intensity of optically thin dust emission: Iν = τν Bν(T). Expand τν κ µ Iν = ν [Dust/Gas] mH NH Bν(T). 2 where κν is the opacity of the dust material, in cm /gm. Dust is mixed with gas. 2 Define another opacity σν, in different units cm /H, a property of the dust + gas mixture. σ κ µ τ ν = ν [Dust/Gas] mH = ν /NH. Changes of dust opacity Evidence for opacity changes Locus of constant Power. Equilibrium Tdust adjusts in response to opacity. Planck early results. XXIV. Dust in the diffuse interstellar medium and the Galactic halo @ 1200 GHz Where does evolution begin? σν = τν /N Alternatively, in the atomicH medium, starting with what emerges from the dense molecular phase. @ 1200 GHz We do see evolution even in the atomic phase. Constant IVCs show evidence of grain destruction. “Metals” returned to theHerschel: gas phase opacity (depletion undone). increases with density. Roy et al. 2012 from 2MASS E(J-Ks) Adopted by Herschel GBS/ HOBYS Planck XXIV 2011 BLAST Martin et al. 2011 Adopted by Herschel GBS/ HOBYS Planck XXIV 2011 Roy et al. 2012 BLAST Martin et al. 2011 Impact on masses Need to know the appropriate value of the opacity to convert dust optical depth to gas column density. τ σ NH = ν / ν. Masses of compact objects (cores, clumps, filaments) extracted from submillimetre maps, and thus our assessment of their gravitational state, are affected (depend inversely on adopted opacity). Motivated by Planck: another probe of dust – scattered light in the optical Light scattering by high-latitude dust The integrated light from stars below in the Galactic plane illuminates the cloud (Sandage 1976). The brightness is a fraction of a percent of the terrestrial night sky, but structure can now can be brought out easily with modern optimally-coated fast lenses in front of CCD detectors. Scattered light: new horizons Higher spatial resolution (3” to 6”) for studies of morphology. A consistency check on the strength of the interstellar radiation field that powers the dust emission. Scattering is sensitive to the amount of dust and grain size and composition a new handle on dust evolution in regions where we see opacity changes in the submillimetre (including dust in “dark gas” regions) but where we can’t get corresponding extinction data because column densities are so low. Trial target: an “IVC” crashing into the Galactic disk DRACO nebula. Scattered light already detected: POSS and Witt 2008. One of our Planck/GBT regions: Planck early results. XXIV. See also poster P26 Lenz. Herschel imaging offers higher resolution, an opportunity to examine the “working surface.” Development of instabilities. Transition between atomic and molecular gas. EmissionDraco IVC, thermal by spinning dust emission. dust Herschel, 250 microns, 20” resolution. W. Erickson 1957 Miville-Deschênes, Boulanger, Martin… F. Hoyle and C. Wickramasinghe 1970 Some observational evidence --> Draine and Lazarian 1998 Planck Herschel zoomed in for detail W.
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